1. Field of the Invention
This invention relates to sealed, multiple-pane glazing units and particularly to the solving of problems of window condensation therewith.
2. Description of the Prior Art
Conventional multiple-pane glazing units consist of two or more parallel sheets of glass which are typically spaced apart from each other using a peripheral spacing-and-sealing assembly. This peripheral assembly conventionally consists of an inner hollow metal spacer filled with desiccant-bead material and an outer hermetic-seal made from sealant material which adheres to the glazing sheets and the back face of the metal spacer. To reduce radiation heat loss, the glazing units can incorporate a low-emissivity coating which is applied to one of the glazing sheets and to further reduce conductive heat loss from the glazing, the cavity between the glazing sheets can also be filled with low-conductive gas such as argon. Conductive heat loss through the spacing-and-sealing assembly can also be reduced by replacing the conductive metal spacer with an insulating spacer.
As disclosed in U.S. Pat. No. 4,831,799 issued to Glover et al., one advantage of substituting an insulating spacer is that the cold-weather problem of edge-of-glass condensation is diminished. However, experience has shown that although the substitution of an insulating spacer substantially reduces conductive heat loss through the perimeter edge seal, condensation at the bottom edge-of-glass area can still occur particularly if there is extreme cold weather and high interior humidity levels. These cold bottom-edge temperatures are primarily caused by convective flow of the air or gas fill within the high thermal-performance, double-glazed units. Further at extreme cold temperatures, this problem of cold-bottom edge temperatures caused by convective flow within the sealed unit cavity becomes particularly significant.
In the past, various assemblies have been incorporated within the double-glazed unit and although typically these assemblies were added for mainly aesthetic reasons, these assemblies also tend to interfere with convective flow within the unit. Listed below are examples from the prior art.
U.S. Pat. No. 49,167 issued to Stetson, describes the use of wood studs which are incorporated in the sealed unit to prevent the center parts of the glazing sheets from coming in contact with each other.
U.S. Pat. No. 2,132,217 issued to Neuendorf, describes a muntin-bar grid incorporated between glazing sheets in order to give the appearance of divided lights and this mutin-bar grid creates a series of small unsealed dead-air spaces and as a result, convective flow within the sealed unit is reduced to some degree.
U.S. Pat. No. 2,915,793 issued to Berg, describes a sealed glazing unit incorporating a venetian window-blind assembly suspended between the glazing.
U.S. Pat. No. 4,091,592 issued to Berlad et al describes a window pane construction consisting of a series of closely-spaced plastic horizontal strips designed to prevent convection currents from developing in the space between the two panes. The window assembly described by Berlad is not a sealed unit and cannot be filled with a low conductive gas such as argon. Further, it should be noted that as with the other previously described additions to the air space, the horizontal film strips do not specifically address the issue of condensation along the bottom edge of the sealed unit. Also, the closely-spaced horizontal strips create visual distortions and obstruct exterior window views.